A monopulse-type antenna device used for detection of a direction in which a target exists, and so on is typically comprised of: a plurality of sub array antennas each including a plurality of element antennas for receiving signals and a plurality of phase shifters for adjusting the excitation phases of the element antennas; a phase shifter controlling unit for controlling the plurality of phase shifters; and a monopulse comparator for forming a radiation pattern which is a sum pattern by in-phase combining the received signals of the plurality of sub array antennas, and for also forming a radiation pattern which is a difference pattern by out-of-phase combining the received signals of the plurality of sub array antennas.
In a monopulse-type antenna device, because the accuracy of detection of targets degrades due to the influence of unnecessary waves, it is necessary to reduce the sidelobes of a sum pattern and the sidelobes of a difference pattern, the sum and difference patterns being formed by the monopulse comparator.
When forming a sum pattern, the sidelobes are reduced in many cases by controlling the amplitude of the received signal of each of the element antennas, to provide an aperture distribution having an amplitude taper. A problem is, however, that when forming a difference pattern by using this aperture distribution, the sidelobe levels of the difference pattern become high.
The following Patent Literature 1 discloses an antenna device in which a power supply circuit is divided into two portions respectively corresponding to a central portion and a perimeter portion of a plurality of element antennas, and two monopulse comparators are disposed independently for the central portion and the perimeter portion.
In this antenna device, while when forming a sum pattern, a reduction in the sidelobes is accomplished by using the above-mentioned aperture distribution having an amplitude taper, when forming a difference pattern, by using only the received signals of the antenna perimeter portion, a distribution having a low amplitude in the antenna central portion is generated as an aperture distribution suitable for a reduction in the sidelobes of the difference pattern, and a reduction in the sidelobes of the difference pattern is accomplished by using the aperture distribution.
Further, the following Patent Literature 2 discloses a technique for generating an aperture distribution which is the average of an aperture distribution suitable for a reduction in the sidelobes of a sum pattern, and an aperture distribution suitable for a reduction in the sidelobes of a difference pattern, and controlling the amplitudes of element antennas by using the averaged aperture distribution, by means of a variable attenuator, thereby accomplishing a reduction in the sidelobes of the sum pattern and in the sidelobes of the difference pattern. A feature of this technique is that the scale of the power supply circuit does not become large.